You and me both. I asked a similar question a week ago and got 0 responses. I've been looking at them and looks like you want one that comes with the 110V adapter. For the most part they all seem to be the same except the pixel perfect vs. 5 dead pixel guarentee. The 550ti should work, but I wouldn't expect it to game well.
Yeah this computer won't be used for gaming much other than the occasional Civilization 5. My main PC is what will play all my games.